Fuel injection pump for internalcombustion engines



Jan. 9, 1951 EVANS ET AL 2,537,748

FUEL INJECTION PUMP FOR INTERNAL-CGMEUSTION ENGINES Filed May 12, 1948 2 Sheets-Sheet l HA I,

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FUEL INJECTION PUMP FOR INTERNAL-COMBUSTION ENGINES Filed May 12, 1948 2 Sheets-Sheet 2 trap air during the return ton, and thus constitute Patented Jan. 9, 1951 OFFICE FUEL INJECTION PUMP QOMBUSTION FOR INTERNAL- ENGINES Arthur Frederick Evans and Stanley Hopkins,

Brentford, England Application May 12, 1948, Serial No. 26,596

In Great 4 Claims.

This invention relates to a fuel injection pump for injecting fuel into the cylinde of an internal combustion engine of the type comprising an in" jection plunger operated, through the agency of a servo piston connected to the injection plunger, by air pressure derived from the engine cylinder, the servo piston executing a forward stroke, to cause the injection plunger to deliver fuel to the engine, under the action of the air pressure and being returned by a return spring.

According to the invention the face of the servo piston exposed to the air pressure and the cooperating end wall of the servo cylinder are formed with complementary stepped parts so arranged that, at the start of the forward stroke of the servo piston the air pressure acts on part only of the area of the servo piston, so that initial movement of the servo piston is slow, the air pressure acting on the full area of the servo piston only after the latter has moved forward a distance determined by the configuration of the stepped faces of the piston and cylinder,

The provision of these complementary stepped parts serves to delay the injection of the fuel and, in the case where the servo piston is permanently exposed to the air pressure, they will act as the timing device for determining the point in the engine stroke at which injection will commence.

.In the case of larger engines, where an air timing valve is provided for exposing the servo piston to the air pressure in the cylinder at an ap propriate point in the engine stroke, the complementary stepped parts will act as a safety device to prevent serious premature injection in case the air timing valve should stick in the open position. 7

The complementary stepped portions serve to stroke of the servo pisa dashpot on the return stroke as well as a safety device on the forward stroke.

Further features of novelty, to be described in detail below, are

(a) the provision of a dashpot or dashpots for retarding the injection plunger towards'the end of its delivery stroke,

Britain March 10, 19.47

in a sleeve drilled 1 main servo piston (b) .the provision of articulation between the servo piston and injection plunger,

(0.) a hydraulic timing gear for operating an air timing valve, which timing gear also Serves to lubricate the servo piston,

- (d) a fuel oil circuit which serves to cool the working parts.

In the. pump about to be described in detail, the iniection plunger is a solid plunger operati i with holes for the admission of fuel to the space in front of the plunger. It is to be understood, however, that in suitable cases the injection plunger may be of annular form and mounted to slide on a fixed piston.

One form of fuel injection pump according to the invention will now be described in detail, by way of example, with reference to the accompany.- ing drawings, in which:

Figs. 1 and 1A, taken together, constitute a front elevation of the injection pump, the injecr s o n n his A fi n nea h e ar o t ap a at s ow i l. as in ed. in chain-dotted lines at the bottom of Fig. 1 and at the top f F A,, and

Figs. 2 and 2A are respectively longitudinal sections taken on the line IIII on t n I -I A i Fi A-v The injection pump is constituted by a unit a d to fi i a l n th t f th n ine cylinder. The unit (see in particular Figs. 3 and 2A) c m r s s the f o n ma n pa t h ch ad ne anothe in the order rec d, tar ng from the top: I

(i) A valve casing IQ with an air inlet I for Connection o th en ne. c linde a c ntainin a horizontally movable air timing valve I? norl y h ld os by a s i3 u assoc ated h a ser p nger. 4 f open n it.

(ii) A vertical servo cylinder [5 containing a {6 and communicating with the valve casing ID by a passage i1 controlled by the air timing valve 12.

ii A cal pump chamb r [-8. ontainin the injection plunger I9, and the fuel inlet and fuel delivery control means, the injection plunger projecting at its upper end into the servo cylinder l5 and being connected to the main servo piston I5.

(iv) A vertical injector body 20, connected to the pump chamber I8 and containing a delivery valve 2!, a filter 22 and a check valve 23.

' (v) A cap 24, containing the jet 2 5, and screwed to the lower end of the injector body 20.

The valve casing i0 is secured to the servo cylinder i5 by nut and bolt connections 26 (Fig. l),

and the servo cylinder 15 is connected to the pump chamber 18 b bolts 21. The injector body 26 is connected to the pump chamber 18 by a thimble 28 having an internal screw thread engaging a screw thread on the lower end of the p cham r '8 and an external scr w t read e ga in a s re h ea a he to f the n ector body 20.

he func on of. the air timin valve 2 s to in Fig. i. and

3 admit to the main servo piston compressed air from the engine cylinder, at pressures from four to five hundred pounds per sq. in., as and when required. The first condition is that the valve 12 should open rapidly in order that full pressure should be available when the piston moves. The timing of this valve l2 relatively to the engine stroke must be correct and this timing should be adjustable.

The air timing valve l2 could be operated mechanically, but in the pump under description it is operated hydraulically, by means of the servo plunger M, which is in alignment with the valve stem and at the end thereof remote from its head. A spring normally maintains the end of the servo plunger clear of the stem of valve 52.

On the engine cam shaft is arranged a cam with a suitable phase adjustment and this operates a spring loaded plunger which delivers oil to a deliver pipe. A tappet lever and roller are interposed between the cam and the plunger and this lever has an adjustable fulcrum that enables fine phase adjustment to be accomplished. This displacer, as it may be considered, is supplied with lubricating o'l from the engine circuit via a filter. The displacer is arranged with a considerable delivery excess beyond the actual bore and stroke requirements of the servo plunger associated with the air timing valve.

The displacer is not illustrated, but the delivery line communicates with an inlet 3% in th valve chamber l0, and the displacer plunger periodical- 1y develops a pressure wave in the oil in the delivery line, and thereby efiects movement of the servo plunger 14 to open the air timing valve Hi. The required lift of the air timing valve 12 will be accomplished some tim before the pump plunger l9 has finishedits deliver stroke but at a designed point, where sufficient lift has been given to the air timing valve l2, the servo plunger l4 uncovers a spill port by reason of its left hand end (Fig. 2) passing to the right of the flange 32 of the chamber 33, and the remainder of the delivery enters the servo plunger chamber 33. It will be realised that while the motion of the servo plunger has been arrested, it cannot retract because of the oil pressure acting on its left hand end face. Therefore this arrangement assures a constant motion to the air timing valve.

The excess oil entering the servo plunger chamber 33 accumulates until its normal leve1 makes contact with the air timing valve spring 13 and by this means is splashed on to the stem of the Valve l2 and thereby provides adequate lubrication for this valve which is never at a ver high temperature.

As the oil enters this chamber the pressure will rise and the surplus oil, plus any air that may leak through the air valve stem, will pass, via a port 34, to a connection 35 that leads to the vicinity of the main dashpot described later.

When the air timing valve 12 opens, compressed air from the cylinder is admitted from th in et II to the passage l! which leads to, and is in axial alignment with, the servo cylinder I5. On the upper end wall of the servo cylinder is fixed a spigot 36, having a central bore 31 registering with the air passage l1. On the adjoining upper face of the servo piston i6 is mounted a socket 38 which, when the servo piston has completed its return stroke, fits over the spigot 36. initially therefore the air pressure is applied only to an area of the servo piston equal to the area of the bore 31 in the spigot 36. As soon however as the cfirvn niston has moved forward sufficiently to clear the socket 33 from the spigot 36, the air pressure is applied to the full area of the servo piston and rapidly accelerates it. On the return stroke of the servo piston, air is trapped as the socket 38 moves over the spigot 36 to act as a dash-pot and cushion the return stroke. The outer wall 39 of the spigot 36 is given a slight taper, converging in a downward direction, to enable the air compressed in the space surrounding the spigot to escape gradually, through the space between the socket 38 and spigot 36, into the bore 3'! of the spigot. The moment in the forward stroke of the servo piston at which it will receive full air pressure is influenced by the amount of taper of the spigot, as the provision of a taper will allow air pressure to leak past on the forward stroke and gradually build up behind the parts of the servo piston outside the socket. If therefore the taper is sufiicient, full air pressure will develop over the servopiston before the socket is entirely clear of the spigot.

The lower face of the servo piston has a central projection 48 having a flat end which flat surface of a hemispherical ball member 4|, the curved face of which rests in a correspondingly shaped socket 42 in the upper end of the injection plunger 19. This upper end has an enlarged shoulder 43, against the lower face of which fits a spring plate 44 by which the pressure of a return spring 45 is applied to the injection plunger 19 and serve piston IE. A cap nut 46 is screwed to the spring plate 44, and a small clearance is left between the head of the cap nut and the flat upper surface of the ball member 41.

This connection provides a small degree of articulation between the servo piston l6 and injection plunger 19, which accommodates for any small inaccuracies in alignment between them, since the servo piston it can float on the plunger 19, while the flat face of the ball member 4| ensures axial loading and a surface contact with the projection 40 on the servo piston.

Into the lower end of the servo cylinder projects a gland housing 41, which is constituted by an upward extension of the pump chamber i8 and forms the lower abutment for the return spring 45. Inside the gland housing 41 are a gland 48 and a steady bush 49 for the injection plunger. The upper end of the gland housing 41 is of reduced external diameter, and surround ing this reduced portion is a steel ring 50, the space between the ring and the reduced portion forming an annular groove 5| into which an annular piston 52, provided on the undersurface of the spring plate 44, moves on the forward stroke of the injection plunger 49. These cooperate to form a dashpot for decelerating the injection plunger 9 at the conclusion of its forward stroke. This is necessary because, at conditions below full throttle, a spill port is opened, as later described, to terminate the injection. Without the dashpot, the servo piston and injection plunger would be accelerated to a dangerous degree by the continued application of air pressure after the spill port has opened. A secondary dashpot may, also as described later, be provided at the lower end of the injection plunger. The main dashpot is preferably arranged to give a progressively increasing resistance to movement of the parts during the injection stroke by making the annular groove 51 of tapering form so that its width decreases gradually from top to bottom.

The excess lubricating oil, fed as already described from the servo plunger M of the air timrests on the plunger,

ing valve through the connection 35 to the vicinity of the main dashpot, passes up through a passage 53 in the gland housing 41, lubricates the gland 46 and passes thence through a passage 54 into the annular groove of the dashpot. From here it is splashed into the servo cylinder and distributed by the return spring over the skirt of the servo piston. The lubricating oil leaves the system through an outlet 68.

The pump chamber carries at its lower end a pump sleeve within which the injection plunger 19 fits, the sleeve being held in position by the thimble 28. Slidably mounted on the injection plunger H3 at the upper end of the pump body I8 is a delivery control muff 55, which is urged upwards by a spring 55 mounted in compression with the pump chamber, but which can be moved downwardly against the action of the spring by rotation, by means of a finger grip 5.1 (Fig. 1), of a toothed throttle control wheel 58 (Fig. 2) which engages rack teeth 59 on the control muff .55.

The injection plunger has, in its lower end, an axial bore 69 open to the forward or lower end of the plunger and communicating, via radial throughgoing holes iii, 62 with a pair of annular grooves 63, 6 3 in the outer surface of the plunger. In the retracted position of the plunger, the front groove 63 is in register with an internal groove 65 inthe sleeve 10, which communicates by a port 66 with the interior of the pump body l8. Fuel oil is fed under pressure to a pump body as later described, through an inlet 51, so that the axial bore so and the portion of the sleeve 10 in advance of the plunger [9 are filled with oil.

After a short initial forward movement of the the front radial hole 6i is brought out of register with the groove 65 in the sleeve 1|], so preventing oil displaced from in front of the plunger from flowing through the bore. At this point injection commences, the oil pressure in front of the plunger causing the injector valves 2}, 23 to open. During this initial movement of the plunger, the rear annular groove 64 in the plunger is blanked off by the control muff 55 and 5.

injection will continue until the rear radial hole 62 clears the forward end of the control muif 55, whereupon oil can flow through the bore 60 in the plunger and back to the pump body through the rear radial hole 62, which acts as a spill port. Injection thus terminates at a point in the forward stroke of the plunger determined by the position of the control muif 55, the remainder of the forward stroke of the plunger being idle since the injector valves 2!, 23 close immediately the rear radial hole 62 is opened. It is during this idle portion of the stroke that the above-mentioned dashpot is effective. The initial idle portion of the stroke, i. e. that portion preceding the closing of the front radial hole 6|, allows the plunger to attain a high momentum prior to opening of the injector valves, thus ensuring that the charge of fuel will be injected into the cylinder at high speed and under high pressure.

The fuel oil should be delivered to the pump from a priming circuit. Oil is taken from the day running tank by means of a small motordriven low pressure oil pump (a suds pump), passed through a suitable fine filter and delivered to a common line serving all the cylinders of the engine and connected to the inlets 61 of all the injection pumps. At the terminal of the line is a spring loaded escape valve loaded to about 10 lb. sq. in. so as to ensure that this pressure is maintained in the system. Each pump has its tapping from this main and the oil enters the pump .at the inlet 61 in the pump chamher and therefore quite high up. Any solid matter that might be suspended in the oil will fall to the bottom out of the way and any free air that may be contained or which may be liberated will immediately rise to the top of the chamber out of the way of the inlet ports to the pump itself. This oil is at a pressure of ten pounds and therefore its velocity will behigh and the surplus fuel oil and any'free air will be carried over through a passage 59 into a jacket 1| surrounding the servo cylinder and then through a passage 12 into an annular cavity 13 in the cylinder to an outlet 14 whence delivered back to the day tank. of the oil serves to cool the working parts of the pump.

It will be understood that the capacity of the priming pump will be at least three times the actual fuel requirements of the engine.

The pump chamber is provided with an inspection plug- 15.

The injector body 29 contains, as already mentioned, the injection valve 29, filter 2E and delivery valve 23, these being the body in that order, injection valve 2! uppermost. The two valves 2!, 23 are of identical construction each comprising a valve head 16, and a valve thimble ii projecting into the bore of a valve seating 18 against which the head 16 is normally held closed by a spring 19. The valve thimble 11 is in the form of a cylinder open at its upper end and having grooves fiii milled in its outer surface, these groves 86 extending from the upper end of the thimble F1 to near the point where it terminates in the valve head It.

The grooves 88 in the valve thimbies are initially full of oil and as soon as the oil pressure on the delivery stroke of the plunger 19 has lifted either valve suihsiently to bring the ends of the grooves 89 in the thimble beyond the seating 18 oil Will flow through the valve. As soon as the spill port 62 opens, the springs 19 of the valves 2i, 23 will return them to their seatings, the cut-off being effected immediately the grooves 83 in the valve thimhles are again masked by their seatings 18.

The above-mentioned secondary dashpot, if provided, is constituted by a spigot (not shown) on the lower end of the injection plunger 19 which passes into the thimble 11 of the injection valve 2i towards the end of the delivery stroke of the plunger. This arrangement will allow a certain amount of oil to be trapped, after the injection valve 2! has closed, in the annulus formed between the spigot and the bore in the thimble, an escape being arranged by making the thimble slightly taper in bore. The oil that escapes through this annulus will pass up the central bore 68 of the plunger to the spill port 62.

What we claim as our invention and desire to secure by Letters Patent is:

1. A fuel injection pump, comprising an injection plunger, a servo piston connected to the injection plunger, a servo cylinder housing the servo piston, a reciprocable air timing valve for periodically admitting to the servo cylinder air pressure to cause forward movement of the servo piston to effect a delivery stroke of the injection plunger, a responsive piston aligned with the air timing valve, a chamber housing the responsive piston and having an inlet for pressure oil and a spill port, a spring for normally holding said mounted in tandem in air timing valve closed, said responsive piston being movable under oil pressure supplied thereto through said inlet to open said air timing valve and, on continued movement under said oil pressure to open said spill port, a gland housing surrounding said injection plunger and having therein an annular groove, an annular piston fitted to the injection plunger and arranged, near the end of the delivery stroke thereof to enter said annular groove to decelerate the injection plunger, a return spring, mounted in compression between said gland housing and said annular piston for returning the injection plunger after the conclusion of the delivery stroke and a conduit for conveying oil from said spill port to a passage in said gland housing communicating with the annular groove therein, the oil fed to said annular groove from said spill port serving to lubricate the servo piston.

2; A fuel injection pump comprising an injection plunger, a servo piston connected to the injection plunger, a servo cylinder housing the servo piston, a jacket surrounding the servo cylinder, an air timing valve mounted to reciprocate in the head of said servo cylinder in a direction transverse to the direction of movement of said servo piston and thereby to periodically admit air under pressure to the servo cylinder to cause forward movement of the servo piston to effect a delivery stroke of the injection plung er, an annular cavity in the head of said servo cylinder surrounding said air timing valve, a fuel chamber surrounding said injection plunger, an inlet for supplying fuel under pressure to said fuel chamber, a variable cut-on gear for determining the quantity of fuel which will be delivered by the injection plunger from said fuel chamber at each delivery stroke of said plunger, conduits for conducting fuel oil from said fuel chamber to said jacket and thence to said cavity to cool said servo-piston and said air timing valve, and a return spring for returning the injection plunger and servo piston after the conclusion of the delivery stroke.

3. A fuel injection pump, comprising an injection plunger, a servo piston connected to the i-- jection plunger, a servo cylinder housing the servo piston, an air-timing valve mounted to reciprocate from an open to a closed position and adapted, when open, to admit pressure air to the servo cylinder to cause forward movement of the servo piston to chest a delivery stroke of the injection plunger, a return spring for returning said injection plunger and servo piston at the conclusion of the delivery stroke, a further spring for normally holding said air-timing valve in closed position, a responsive piston aligned with said air timing valve, a chamber housing said responsive piston and having an inlet for pressure oil and a spill port, said responsive piston being movable under oil pressure supplied thereto through said inlet to open said air timing valve, and, on continued movement under said oil pressure, to open said spill port, and a conduit communicating with said spill port for conveying excess oil to the servo piston to lubricate the same.

4. A fuel injection pump, comprising an injection plunger, a servo piston connected to the injection plunger, a servo cylinder housing the servo piston, an air timing valve mounted to reciprocate from an open to a closed position and adapted, when open, to admit pressure air to the servo cylinder to cause forward movement of the servo piston to eiiect a delivery stroke of the injection plunger, a return spring for returning said injection plunger and servo piston at the conclusion of the delivery stroke, a further spring for normally holding said air timing valve in closed position, a responsive piston aligned with said air timing valve, and a chamber housing said responsive piston and having an inlet for pressure oil and a spill port, said responsive piston being movable under oil pressure supplied thereto through said inlet to open said air timing valve, and, on continued movement under said oil pressure, to open said spill port.

ARTHUR F. EVANS. STANLEY HOPKINS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS- 

